Area forecast discussion
National Weather Service State College PA
1044 PM EDT Friday may 24 2013
Synopsis...
cold air aloft associated with a deep upper low will traverse the
region tonight...bringing unseasonably cool and quite breezy
conditions. Canadian high pressure will build over Pennsylvania
during the Holiday weekend ensuring fair weather. Temperatures
will begin the weekend well below normal but moderate by Memorial
Day.
&&
Near term /until 6 am Saturday morning/...
late evening water vapor loop showing upper trough axis lifting
into eastern PA. Lg scale forcing ahead of trough should support a
few lingering -shra/sprinkles across our eastern counties through
around 06z.
Cross polar flow driving an unseasonably chilly air mass
southward into PA should set the stage for a late season freeze
over portions of the Allegheny plateau tonight. Although not much
radiational cooling is expected tonight due to a persistent northwest
wind...readings already in the u30s over the West Mountains at 02z...so
not much cooling needed for a freeze. Evening infrared satellite imagery
showing clearing skies downwind of Lake Erie...as very dry air
works south into the region. This is despite 800 mb temperatures cold enough
to support lake effect. So...believe skies will clear fairly
quickly between 03z-06z across the western half of the state...while
clouds associated with upper trough linger over the eastern counties.
Will maintain freeze warnings as is for tonight. Highest
probability of a freeze appears to be over the Laurel Highlands
based on latest gefs/sref and high res NAM data. Although gusty
winds will diminish somewhat overnight...a tight pressure gradient
should keep an active northwest breeze going through the night and preclude
frost formation. Therefore only the freeze headlines are hoisted
for tonight.
&&
Short term /6 am Saturday morning through 6 PM Saturday/...
lg scale subsidence and anomalously dry air works over central PA
on Saturday in wake of departing upper low...bringing mostly sunny skies
to much of the region. Temperatures may still be cold enough aloft to
support a more even mix of sun and cumulus across across the
eastern counties...especially Sullivan. However...will keep mention of
rain showers out of the forecast based on aforementioned low precipitable waters and lack of
forcing.
Model soundings show mixing to 800 mb...which should translate to highs
from the m50s high terrain...to m60s susq valley...some 10-15f
warmer than today. As blyr depth increases...expect northwest winds to
become gusty again on Saturday. BUFKIT soundings support gusts in
the 25-30kt range by afternoon.
&&
Long term /Saturday night through Friday/...
we start the extended off dealing with the anomalousy deep upper
low that will be moving slowly through New England and the
coastal waters.
Sunday will be fair and dry...albeit on the chilly side. The dry
weather will continue through Monday as we benefit from the upper
ridge building in from the west. Those two days will start the
extended off in a rather uneventful fashion.
From Tuesday through at least midweek the forecast gets murky as
the building sub tropical ridge over the southern states shoves
the westerlies northward. With US being on the southern edge of
these westerlies/northern edge of the subtropical ridge...we will
become vulnerable to upstream mesoscale convective system development as the heat and
humidity begins to make inroads to the region once again.
Differences in the model timing of these convective complexes is
big with the operational GFS showing a wet day Tuesday...and the
European model (ecmwf) suggesting the convection stays mainly south of here at that
time. Gefs splashes a fair amount of diurnally favored precipitation
around just about every day starting Tuesday. The mean upper flow
and accompanying surface pattern suggest whatever semblance of a
warm front there is passes through on Wednesday...with the
remainder of the week firmly under the influence of the Bermuda
high and warm muggy southwest flow. With the operational
GFS/European model (ecmwf) both predicting a surge in middle level temperatures by later Wednesday
into Thursday...I am thinking we will spend much of the time after
middle week pretty capped leading to hazy hot and humid conditions
with fairly small chances for showers and thunderstorms. I like
our current forecast which downplays the chances for rain after
Wednesday...and will continue along those lines through Friday.
&&
Aviation /03z Saturday through Wednesday/...
an unseasonably strong/deep upper-level trough will rotate eastward
from the lower Great Lakes/Ohio Valley through the middle-Atlantic and northeast
states over the next 48-72 hours. A cold and blustery north-northwest flow
will accompany widespread stratus/stratocu with MVFR across
the west this evening.
Partial clearing overnight...but it will remain windy.
Expect scattered cumulus on Sat...given cold air aloft. Ipt will likely
go back to broken skies...but VFR...given how dry the air will
be.
Winds will weaken by Sunday...with Monday being the best
day.
Warm advection on Tuesday could set off a few showers or storms...
mainly late. Warmer Wednesday...but still a chance of a shower or storm.
Have a good Holiday weekend.
Outlook...
sun-Mon...VFR. No sig weather expected.
Tue-Wed...scattered thunderstorm impacts possible.
&&
Ctp watches/warnings/advisories...
freeze warning from 2 am to 9 am EDT Saturday for paz004>006-
010-011-017-024-033.
&&
$$
Synopsis...devoir/Fitzgerald
near term...Fitzgerald
short term...devoir/Fitzgerald
long term...la corte
aviation...Martin
